The oxygen reduction reaction mechanism on Sn doped graphene as an electrocatalyst in fuel cells: a DFT study

Heteroatom doped graphene has caused particular interest in recent years due to its promising ORR (oxygen reduction reaction) activity in fuel cells. Sn doped divacancy graphene (Sn–Gra) was predicted to be a good candidate as a cathode catalyst in the previous study. In this work, the detailed ORR mechanism has been studied for Sn–Gra. The calculated charge transfer indicates that Sn and its adjacent four C atoms are the catalytic reaction sites. The unstable intermediate HOOH suggests that Sn–Gra experiences a four-electron ORR process. The most favorite pathway is the hydrogenation of the O2 molecule. The rate determining step is the hydrogenation of OOH to form H2O + O with the energy barrier of 0.75 eV. This value is slightly smaller than 0.80 eV for Pt, implying that Sn–Gra is a potential cathode catalyst for ORR. The predicted working potential is 0.16 V for the most favorite pathway. We expect that this study could provide new insights for the design of low-cost and highly efficient electrocatalysts in fuel cells.